The present invention relates in general to an arrangement for mounting a plurality of circuit chips on a multiple chip unit (MCU), which provides high chip density and efficient cooling and interconnection of the chips.
MCU's are chip mounting structures which contain a plurality of circuit chips, and are often employed to contain the chips in central processors for high performance digital computers. Typically, an MCU includes a multiple layer circuit mounting board which has a plurality of circuit chip mounting sites and associated interconnects and bonding pads for supplying power and control signals to each of the chips. In prior art MCUs, one or more circuit chips are mounted horizontally at each of the chip mounting sites and are connected to bonding pads on the sites by means of conventional TAB lead frames, or the like.
In order to insure that each of the circuit chips of an MCU operates correctly, some means must be provided to remove heat from the chips. In the past, this has been accomplished by providing heat removing structures in the circuit mounting board at each of the chip sites which contact the bottom sides of each of the chips and provide a thermal path for the removal of heat therefrom. These heat removing structures necessarily require space in the chip mounting board which limits the amount of space in the board for the circuit chip interconnects. This places a limitation on the number of circuit chips which can be mounted on an MCU.
As computer technology progresses, the emphasis is on increasing the operational speed or frequency of the computer and a key limitation becomes the time it takes signals to travel from one circuit chip to another. This traverse time is directly proportional to the length of the interconnects between each of the circuit chips and it is thus desirable to mount each of the circuit chips of the computer as physically close to one another as possible to reduce the interconnect lengths. In prior art MCU's, the number of chips is limited by the amount of surface area on the mounting board for each of the circuit chips, as well as by the amount of room available in the board for the heat removing structures and the chip interconnects. Thus, in order to increase the packing density of the circuit chips in an MCU, extra space must be provided not only for the additional circuit chips, but for their interconnects, and a means must be provided to remove the heat generated by the densely packed chips.